Kumar IronThe formula
The weight of a TMT bar in kg per metre is d² divided by 162, where d is the diameter in mm. A standard length is 12 m, so one rod weighs 12 x d² / 162 kg. The formula is based on a steel density of 7850 kg/m³. Rolled bars are allowed a small tolerance in weight under IS 1786, so real rods can be a little over or under.
Example: a 16 mm bar weighs 16 x 16 / 162 = 1.58 kg per metre, so a 12 m rod weighs about 18.96 kg.
Weight per rod and rods per tonne
| Size (mm) | Weight per metre (kg) | Weight of one 12 m rod (kg) | Rods in 1 tonne |
|---|---|---|---|
| 8 | 0.395 | 4.74 | about 211 |
| 10 | 0.617 | 7.41 | about 135 |
| 12 | 0.889 | 10.67 | about 94 |
| 16 | 1.580 | 18.96 | about 53 |
| 20 | 2.469 | 29.63 | about 34 |
| 25 | 3.858 | 46.30 | about 22 |
| 32 | 6.321 | 75.85 | about 13 |
Rods per tonne is 1000 divided by the weight of one rod, rounded.
Rods per bundle depends on the brand
There is no single standard count for a bundle. Each mill ties its own bundle size, and the count differs by brand, plant and diameter. Thin bars such as 8 mm and 10 mm are tied in larger counts, and thick bars such as 25 mm and 32 mm in small counts. So a bundle is not a fixed weight, and you should not price or compare steel by bundles.
To find a bundle's weight, count the rods in the bundle and multiply by the weight per rod from the table. Example: if a bundle of 12 mm bars has 20 rods, its weight is about 20 x 10.67 = 213 kg.
How to check a delivery
- Count the rods per size and multiply by the table weight to get the expected weight.
- Compare with the weighbridge slip or the invoice weight. A small difference is normal because of the tolerance.
- Confirm the rod length. Some bars are cut to 9 m, 10 m or 11 m, which changes the weight per rod. Use length x d² / 162.
- Check the brand marking and grade on the bar, and ask for the mill test certificate.
Why billing is by weight
Because the rod count can differ from the table, a fair bill is always by weight. Ask for the final weight on a weighbridge slip, and the per kg rate. Use our TMT weight chart for quick lookups and the steel calculator to work out how much your house or slab needs.
Frequently asked questions
- How many kg is one 12 m TMT rod?
- About 4.74 kg for 8 mm, 7.41 kg for 10 mm, 10.67 kg for 12 mm, 18.96 kg for 16 mm, 29.63 kg for 20 mm, 46.30 kg for 25 mm and 75.85 kg for 32 mm, calculated with d²/162.
- How many rods are in a bundle of TMT bars?
- It depends on the brand and size. There is no standard count, so count the rods and multiply by the weight per rod.
- How many 12 mm rods make one tonne?
- About 94 rods of 12 m length.
- Is the d squared by 162 formula exact?
- It is a close calculation from the density of steel. Actual bars have a small weight tolerance under IS 1786, so real weights vary slightly.